The Jet
7) It took a small jet 5 hours to make a 1,285 mile trip.
During the last three hours of the flight, it traveled 30 mph slower
than it did during the first two hours. What was its speed for
the first two hours? And what was its speed for the last three
hours?
2x + 3(x-30) = 1285 ("x" = the faster speed. "2x" =
2 hours of the faster speed.)
2x + 3x -90 = 1285
5x -90 = 1285
5x = 1375
x = 275
Since "x" equals 275 (mph), then that is the speed of the jet
during the first two hours, and two hours at that speed was a
distance of 550 miles. When we plug the value of x into the x-variable
for the second term -- 3(x-30) -- we have 275-30, which equals
245 (mph), the speed that the jet traveled for the last three
hours; and multiplying that by the three hours, gives us 735
miles. Adding that to the 550 miles of the first two hours,
totals 1,285 miles; so it checks out fine.